Linux 上创建线程一般使用的是 pthread 库 实际上 libc 也给我们提供了创建线程的函数 那就是 clone
int clone(int (*fn)(void *), void *child_stack,
int flags, void *arg, ...
/* pid_t *ptid, struct user_desc *tls, pid_t *ctid */ );
man 手册里面说的很清楚这个函数存在的意义就是实现 线程 当然这个函数不是 linux 的系统调用 而是对系统调用的封装 。
首先需要给新的线程创建个堆栈 ，使用函数 mmap ,这个函数常用来完成文件映射 这里分配内存也是可以的
void *pstack = (void *)mmap(NULL,
STACK_SIZE,
PROT_READ | PROT_WRITE ,
MAP_PRIVATE | MAP_ANONYMOUS | MAP_ANON ,//| MAP_GROWSDOWN ,
-1,
0);
通过指定 MAP_ANONYMOUS 标识 系统就不会创建文件映射 而仅仅分配内存
注意堆栈不要太小了 不然会溢出的 。。
然后调用 clone 函数
1ret = clone(thread_func, 2 (void *)((unsigned char *)pstack + STACK_SIZE), 3 CLONE_VM | CLONE_FS | CLONE_THREAD | CLONE_FILES | CLONE_SIGHAND | SIGCHLD, 4 (void *)NULL);
注意堆栈是向下增长的 所以指定对战的内存的时候 要使用分配内存的尾部的指针
几个标识的意义
1CLONE_VM (0x100) - tells the kernel to let the original process and the clone in the same memory space; 2 CLONE_FS (0x200) - both get the same file system information; 3 CLONE_FILES (0x400) - share file descriptors; 4 CLONE_SIGHAND (0x800) - both processes share the same signal handlers; 5 CLONE_THREAD (0x10000) - this tells the kernel, that both processes would belong to the same thread group (be threads within the same process);
在线程函数中 直接 return 就可以退出线程了。。。。
使用 clone 的时候 指定 CLONE_THREAD 那么以后就不能使用 wait 来等待这个线程了 相当于 deteched .了。。。查看man 手册可以看到
A new thread created with CLONE_THREAD has the same parent process as the caller of clone() (i.e., like CLONE_PARENT), so that calls to getppid(2) return the same value for all of the threads in a thread group. When a CLONE_THREAD thread terminates, the thread that created it using clone() is not sent a SIGCHLD (or other termination) signal; nor can the status of such a thread be obtained using wait(2). (The thread is said to be detached.)
下面是我测试的代码
1#define _GNU_SOURCE /* or _BSD_SOURCE or _SVID_SOURCE */ 2#include <unistd.h> 3#include <sys/syscall.h> /* For SYS_xxx definitions */ 4#include <sys/types.h> 5#include <sched.h> 6#include <sys/mman.h> 7#include <signal.h> 8#include <stdio.h> 9#include <errno.h> 10#include <string.h> 11#include <sys/wait.h> 12 13#define STACK_SIZE 1024*1024*8 //8M 14 15int thread_func(void *lparam) 16{ 17 printf("thread id %d \n", (int)syscall(SYS_gettid)); 18 printf("thread get param : %d \n", (int)lparam); 19 sleep(1); 20 return 0; 21} 22 23 24void child_handler(int sig) 25{ 26 printf("I got a SIGCHLD\n"); 27} 28 29int main(int argc, char **argv) 30{ 31 setvbuf(stdout, NULL, _IONBF, 0); 32 signal(SIGCHLD, child_handler); 33 //signal(SIGUSR1, SIG_IGN); 34 35 void *pstack = (void *)mmap(NULL, 36 STACK_SIZE, 37 PROT_READ | PROT_WRITE , 38 MAP_PRIVATE | MAP_ANONYMOUS | MAP_ANON ,//| MAP_GROWSDOWN , 39 -1, 40 0); 41 if (MAP_FAILED != pstack) 42 { 43 int ret; 44 printf("strace addr : 0x%X\n", (int)pstack); 45 /* 46 CLONE_VM (0x100) - tells the kernel to let the original process and the clone in the same memory space; 47 CLONE_FS (0x200) - both get the same file system information; 48 CLONE_FILES (0x400) - share file descriptors; 49 CLONE_SIGHAND (0x800) - both processes share the same signal handlers; 50 CLONE_THREAD (0x10000) - this tells the kernel, that both processes would belong to the same thread group (be threads within the same process); 51 */ 52 ret = clone(thread_func, 53 (void *)((unsigned char *)pstack + STACK_SIZE), 54 CLONE_VM | CLONE_FS | CLONE_FILES | CLONE_SIGHAND |SIGCHLD, 55 (void *)NULL); 56 if (-1 != ret) 57 { 58 pid_t pid = 0; 59 printf("start thread %d \n", ret); 60 sleep(5); 61 pid = waitpid(-1, NULL, __WCLONE | __WALL); 62 printf("child : %d exit %s\n", pid,strerror(errno)); 63 } 64 else 65 { 66 printf("clone failed %s\n", strerror(errno) ); 67 } 68 } 69 else 70 { 71 printf("mmap() failed %s\n", strerror(errno)); 72 } 73 return 0; 74}